Analysis of spontaneous subthreshold activity in spinal motoneurons of the cat.

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Abstract
Spontaneous subthreshold potentials in lumbar motoneurons of the cat were recorded with intracellular electrodes. The variations of the amplitude of spontaneous potentials could not be accounted for by spatial attenuation or by coincidences of more than 2 unit potentials. The unit synaptic potentials appear to be equal at different synaptic contacts. The spontaneous potentials remaining in the presence of tetrodotoxin showed a normal amplitude distribution with a mean of about 0.2 mv. There was no enhancement in the spontaneous activity by excess K after application of tetrodotoxin. Spontaneous potentials larger than 0.4 mv are due to background impulse activity and the true miniature synaptic potentials correspond in amplitude to the unit potentials which make up the normal synaptic response.